Teaching Case

A healthy 61-year-old woman was referred to our hospital because of incidental detection of a liver mass during abdominal US performed for evaluation of right upper quadrant pain. She had unremarkable physical and laboratory evaluation.
An upper abdominal MDCT and MR with intravenous contrast injection were performed.

Pre-contrast CT showed an isoattenuating lesion. At contrast-enhanced CT the lesion showed brisk heterogeneous enhancement in the arterial phase. On portal and delayed phases, there was persistent hyperenhancement without wash-out.
MR showed a hypointense T1 and T2 lesion with marked progressive enhancement throughout the liver enhancement phases.

Imaging findings were not consistent with typical benign lesions such as haemangioma or focal nodular hyperplasia or malignant lesions such as hepatocellular carcinoma or metastasis. A differential diagnosis including atypical adenoma, peripheral cholangiocarcinoma, or stromal tumour was suggested.
US-guided biopsy was performed. Histological specimen disclosed benign mesenchymal proliferation with a small number of spindle cells without necrosis or mitotic figures. At immunohistochemical examination, the lesion was positive for actin. The lesion was diagnosed as a probable hepatic leiomyoma.
The patient underwent a left hepatectomy.
On gross examination, the resection specimen showed a pinkish-white fasciculated well-delineated subcapsular mass of 9.5 x 9 x 6 cm with hard elastic consistency (Fig. 3).
At histological examination it was composed by spindle cells without atypia. There were no foci of necrosis or mitosis (Fig. 4). At immunohistochemical examination, the lesion was positive for actin (Fig. 5).
The final diagnosis was hepatic leiomyoma and four years later there is no evidence of tumour recurrence.
Primary smooth muscle tumours are uncommon, especially leiomyoma and there are few cases reported in the literature [1].
Characteristic histological features are spindle cell proliferation with elongated nuclei, eosinophilic cytoplasm, no nuclear atypia, haemorrhage or necrosis. In some cases, a fibrous capsule is described. Immunohistochemical examination demonstrates positive staining for smooth muscle actin.
The lesions were generally described as a markedly hypervascular lesion [2]. There was more variability in ultrasound findings, although a hypoechoic appearance was the most frequent. Reported CT features include brisk enhancement in the arterial phase, mainly peripheral and in some cases a persistent enhancement in portal and delayed phase. On MR, leiomyoma is usually hypointense on T1-weighted images and hyperintense on T2-weighted images. There are some descriptions of isointense or hypointense signal on T2 [3]. After administration of contrast material, it usually shows an enhancement pattern similar to CT and no enhancement with liver-specific MR contrast agents [4].
In the few cases reported, imaging examination did not allow for a confident presurgical diagnosis and percutaneous biopsy did not yield significant information, usually leading to surgical resection.
Surgical resection proved to be both diagnostic and curative in the reported cases [5].